1. Field of the Invention
The present invention relates to an optical imaging module and more particularly to an optical imaging module used in portable devices.
2. Description of the Prior Art
In recent years, the development of the optical lens module in digital cameras, web cameras and portable phone cameras becomes more rapid with the sharp increase in demand of people for high image capturing quality. High resolution, large field of view for sub camera, smaller size and etc are all considered more and more by consumers.
Generally, for the sake of meeting customers' demands, especially demands for high imaging resolution a conventional lens module is used to be a three-lens structure or a four-lens structure. But now the conventional structure was no longer capable to accomplish the mission, since the aberrations and the total track length of the optical system thereby cannot be further modified while achieving a high resolution or a larger field of view. Meanwhile, the manufacturer found it hard to maintain a high yield of lens module when trying to pursue a relative high imaging quality since the aspheric coefficients of lens elements are not preferable yet. Besides, the defocus state of a lens module will significantly influence the performance of the whole camera in auto-focusing, which was confirmed by the assembling factory.
How to achieve a quick focusing module with less aberrations, and balance the weight between high imaging quality and manufacturing feasibility is the key topics in lens module fabrication, therefore, there is need to construct a favorable lens module structure with a good adjustment of its structure and aspheric coefficients.
A patent CN202794682 discloses an optical imaging module which comprises five lens elements and at least a plat element, wherein the first lens element with positive refractive power has a convex object-side surface, the second lens element has negative refractive power, the third lens element, the fourth lens element and the fifth lens element are all have refractive power. This invention can achieve a shorter TTL by applying a plat element made by larger coefficient of linear thermal expansion. But the invention is not conducted through adjusting relationships between aspheric coefficients, not performed with a good defocus state either.